Migration Of Self-interstitial Atoms Research Articles

Migration mechanisms of mono-/di-interstitials in vanadium with alloying Ti/Cr

Self-interstitial atoms (SIAs) are the dominant self-defects at equilibrium in metals, but many questions such as their diffusion characteristics are still open, and studies of the Ti/Cr effect on the kinetics of SIAs are very scarce in vanadium alloy. In this work, we systemically investigated the migration mechanisms of mono/di-interstitials as well as the effect of alloying elements Ti/Cr on the kinetics of SIAs using first-principles calculations. The findings reveal that 〈111〉SIA exhibits three migration mechanisms, including one dimensional (1D) migration, translation-rotation and translation, corresponding energy barriers of 0.008, 0.19 and 0.44 eV. Different migration pathways are activated at high temperatures, which supports the experimental observation of 3D migration of SIAs under high temperatures. We determined the di-SIA (two parallel 〈111〉SIA) migration by both successive and simultaneous jumping paths, the lowest migration barrier is 0.009 eV via successive jumping path passing a translation state. Moreover, based on three migration mechanisms of SIA, SIA migrating to Ti region possesses the lower barrier than pure vanadium, in verse the barrier is relative high and then hinders the SIA diffusion. The alloying Ti has a pinning effect on SIAs. And we explored how SIA to form mixed V-Cr interstitial and its migration of 〈111〉V-Cr. Finally, we estimated the effect of Ti on SIA diffusivity by empirical formulas.

Rotation and migration behavior of self-interstitial atoms in 3C-SiC: A comprehensive ab initio study

First-principles calculations were carried out to investigate the stable and potential metastable structure of neutral and charged self-interstitial atoms (SIAs) in 3C-SiC. Besides, we have systematically studied the most likely rotation and migration paths of these SIAs. The calculated activation energy for the full space rotation of C, C2+, Si and Si4+ interstitials are 0.48 eV, 0.59 eV, 0.73 eV and 0.43 eV, respectively. The migration energy barrier for the long-distance diffusion of C, C2+, Si and Si4+ interstitials are 0.71 , 1.57 , 0.73 and 3.15 eV. The charge state can not only affect the energy barrier of SIAs but also change the migration path. In general, this work can provide a comprehensive picture describing the full space rotation and long-distance migration of SIAs, and the energy barriers in this work are in good agreement with previous defect annealing experiments and simulation results.

Collaborative motion of helium and self-interstitial atoms enhanced self-healing efficiency of irradiation-induced defects in tungsten

Helium (He) is a typical impurity element and plays a crucial role in the microstructural evolution in nuclear materials under irradiation. Here, we systematically investigate the interactions between He and self-interstitial atoms (SIAs) as well as their influences on the kinetic behaviors of SIAs in tungsten (W), using both first-principles and object kinetic Monte Carlo methods. It is found that there are attractive interactions between He and SIAs, which become stronger with the increasing of SIA numbers. Specifically, the He-SIA1 and He-SIA2 complexes adopt a three-dimensional (3D) migration pattern with an effective energy barrier of 0.38 and 0.61 eV, respectively, which is completely different from the 1D migration of SIAs in W (⩽0.033 eV) without He. Such an unexpected collaborative 3D motion of He-SIA complexes increases the probability of vacancy-interstitial recombination and reduces the number of surviving defects. Consequently, our calculations reveal the enhanced effect of He on the self-healing efficiency in W, which is originated from the collaborative 3D motion of He-SIA complexes. The current results can improve our fundamental understanding of the influence of He on the evolution of irradiation defects and have great implications to estimate the performance of W-PFMs in fusion environment.

Investigation of Migration and Transformation of Self-Interstitial Atoms in 3C-SiC via DFT Calculations

First-principles calculations were carried out to investigate the stable and potential metastable structure of self-interstitial atoms (SIAs) in 3C-SiC. The most stable C and Si interstitials we obtained are Ci-C and Sii-Si split interstitials, respectively. In addition, a serious of metastable structures Ci-C (x = 0.63 ~ 0.81), Ci-C , Ci-Si , Sii-Si and Sii-Si have been observed. The migration and transformation of these SIAs were systematically studied. The minimum migration barrier for the full space rotation of C and Si interstitial are 0.49 eV and 0.73 eV, respectively. For the long-distance migration of SIAs, the minimum migration energy for C and Si interstitials is 0.71 eV and 0.73 eV, the corresponding migration paths are Ci-C(2 ‾5‾ 2) ↔ Ci-Si(1 1 6) ↔ Ci-C(‾5‾ 2 2), and Sii-Si ↔ SiTC ↔ Sii-Si .

Collaborative Motion of Helium and Self-Interstitial Atoms Enhanced Self-Healing Efficiency of Irradiation-Induced Defects in Tungsten

The self-healing of nuclear materials is dependent on the motion pattern of irradiation-induced defects. Helium (He) is a typical impurity element in nuclear materials and plays a crucial role on the microstructure evolution under irradiation. Here, we systematically investigate the interactions of He with self-interstitial atoms (SIAs) in tungsten (W) as well as their influences on the kinetic behaviors of SIAs and defects annihilation, using first-principles method and object kinetic Monte Carlo calculations. It is found that there are attractive interactions between He and SIAs, which become stronger with the increasing of SIA numbers. Therefore, He has significant effect on the migration behaviors of SIAs in W. Specifically, the He-SIA1 and He-SIA2 complexes adopt a three-dimensional (3D) migration pattern with the energy barrier of 0.38 and 0.61 eV, respectively, which is completely different from the fast 1D migration of SIAs in W (≤ 0.033 eV) without He. Such unexpected collaborative 3D motion of He-SIA complexes increases the probability of Frenkel pairs recombination and reduces the number of surviving defects. Consequently, our calculations reveal the enhancing effect of He on the self-healing efficiency in W, governed by the concerted 3D motion of He-SIA complexes. These will improve our fundamental understanding of the influence of impurities on the evolution of irradiation defects in nuclear materials.

What promotes derected self assembly (DSA)?

A low-energy electron beam (EB) can create self-interstitial atoms (SIA) in a solid and can cause directed self-assembly (DSA), e.g. {311}SIA platelets in c-Si. The crystalline structure of this planar defect is known from experiment to be made up of SIAs that form well aligned 〈110〉 atomic rows on each (311) plane. To simulate the experiment we distributed Frenkel pairs (FP) randomly in bulk c-Si. Then making use of a molecular dynamic (MD) simulation, we have reproduced the experimental result, where SIAs are trapped at metastable sites in bulk. With increasing pre-doped FP concentration, the number of SIAs that participate in DSA tends to be increased but soon slightly supressed. On the other hand, when the FP concentration is less than 3%, a cooperative motion of target atoms was characterized from the long-range-order (LRO) parameter. Here we investigated the correlation between DSA and that cooperative motion, by adding a case of intrinsic c-Si. We confirmed that the cooperative motion slightly promote DSA by assisting migration of SIAs toward metastable sites as long as the FP concentration is less than 3%, however, it is essentially independent of DSA.

Activation energy for long-range migration of self-interstitial atoms in tungsten obtained by direct measurement of radiation-induced point-defect clusters

The activation energy for the long-range intrinsic migration of self-interstitial atoms (SIAs) in metals, , is an important physical quantity closely associated with microstructural evolution upon energetic particle irradiation. The values for various metals have been widely investigated through recovery experiments on specimens irradiated at low temperatures upon thermal annealing, and the values have been estimated from the dependence of measured quantities of the specimens on the annealing temperature. On the other hand, the dependence of measured quantities on irradiation temperature is also expected to reflect the values. It is of importance to compare the values obtained by these two different kinds of experiments. However, no systematic studies have been carried out along the latter line. In this study, the number densities of SIA clusters formed in tungsten upon high-energy electron irradiation are directly measured as a function of the irradiation temperature using high-voltage electron microscopy. The analysis of the experimental data shows that the value is in the range from 0.088 to 0.102 eV or it is less than 0.046 eV. These values are consistent with those obtained in a recovery experiment and a theoretical study, respectively.

Stability and Mobility of Mono- and Di-Interstitials inα-Fe

We report a detailed ab initio study of the stability and migration of self-interstitial atoms (SIAs) and di-interstitials (di-SIAs) in alpha-Fe. The <110> dumbbell is confirmed to be the most stable SIA configuration, 0.7 eV below the <111> dumbbell. The lowest-energy migration path corresponds to a nearest-neighbor translation-rotation jump with a barrier of 0.34 eV. The most stable configuration for di-SIAs consists of <110> parallel dumbbells. Their migration mechanism is similar to that for SIAs, with an activation energy of 0.42 eV. These results are at variance with predictions from existing empirical potentials and allow one to reconcile theory with experiments.

Computer Simulation of the Migration Of Self-Interstitial Atoms in Alpha-Zirconium

AbstractThe migration of single interstitials and small interstitial clusters in ox-zirconium at different temperatures has been analysed using a molecular dynamics model with a many-body interatomic potential. The migration exhibits a strong anisotropy. The defects are very mobile (with Em = 0. 01 eV) along &lt;1120&gt; directions in the basal plane, and this motion is dominant for the single interstitial at low temperature and the di- and tri-interstitials at all temperatures. Above about 500 K, the single interstitial exhibits 2-D and 3-D motion, but Em for non-basal motion is about 0.133 eV. These results point to important consequences for the behaviour of defects formed by displacement cascades in irradiated zirconium.

Migration mechanism of self-interstitial atoms in Mo after low temperature irradiation II. Dislocation pinning

Dislocation pinning due to 〈110〉 self-interstitial atoms (SIAs) in Mo after 20 MeV proton irradiation at 5 K was investigated in the wide range of Frenkel-pair concentrations C FP from 10 −4 to 10 ppm, where dislocation pinning due to the free migration of SIAs is observed as a broad pinning at around 40 K (the so-called 40 K pinning). With increasing C FP, the magnitude of the 40 K pinning increases showing a shift to lower temperatures. Close study suggests that the 40 K pinning is composed of a constituent lower temperature pinning (LTP) and higher temperature pinning (HTP). The fractional ratio of SIAs arriving for LTP to those for the whole 40 K pinning F LTP increases with decreasing C FP, showing saturation at 100% for C FP below 0.001 ppm, or decreases in proportion to C FP 1/3 for C FP⩾0.001 ppm. The C FP dependence of F LTP is very similar to the fractional ratio of SIA-Is in C FP reported in Part I, where SIA-Is are 〈110〉 SIAs which can undergo three-dimensional migration. The C FP dependence of SIAs of another type responsible for HTP is very similar to that of SIA-IIs reported in Part I which reveal no relaxation peak, suggesting that SIA-IIs cannot undergo three-dimensional migration but migrate two or one dimensionally. The present work suggests that 〈110〉 SIAs of two types can be formed in Mo during low temperature irradiation.

Direct Observation of Uncorrelated Long-Range Migration of Self-Interstitial Atoms in Ordered Alloys

Direct Observation of Uncorrelated Long-Range Migration of Self-Interstitial Atoms in Ordered Alloys

The stage ii recovery behavior of a series of ion-irradiated platinum (gold) alloys as studied by field-ion microscopy

Abstract Direct and visible evidence has been obtained for long-range migration of self-interstitial atoms (SIAs) in Stage II of three different ion-irradiated platinum (gold) alloys. Field-ion microscope (FIM) specimens of Pt-0.10, 0.62 and 4.0 at.% Au alloys were irradiated in situ with 30 keV W+ or Pt+ ions at a tip temperature of 35 to 41 K at 2 × 10−9 torr. Direct observation of the surfaces of the FIM specimens during isochronal warming experiments to 100 K showed that a flux of SIAs crossed the specimens' surfaces between 40 to 100 K. The spectrum for each alloy consisted of two recovery peaks (substages IIB and IIC).The results are explained on the basis of an impurity-delayed diffusion mechanism employing a two-level trapping model. The application of this diffusion model to the isochronal recovery spectra yielded a dissocation enthalpy (δh diss li-Au) and an effective diffusion coefficient for each substage; for substage IIB δh diss li-Au (IIB) = 0.15 eV for substage IIC δh diss li-Au (IIC) = 0....